I meant for software in general; I guess you don't agree? My reasoning is that you have to think systematically about what can go wrong in order to be a good programmer, which is a skill that you can only acquire by finding bugs in programs.

No, I don't agree. I think in many cases it's possible to code defensively without having what my partner Dave calls "killer instinct", the X-factor for being good at finding vulnerabilities in systems. Also, good breakers have to deal with arbitrary technologies; a good developer can specialize, substituting experience and depth of knowledge for intuitive feel.